The invention relates to a connection between a device in a metallic sheath insulated by a gas under pressure and a transformer insulated by a dielectric liquid similar to those described in French Pat. No. 2,223,801. Such a connection comprises a jacket separating the interior volume of the transformer from that of the device, the interior volume of the jacket being filled with a dielectric liquid at a pressure close to atmospheric pressure and delimited by two surfaces: an interior surface and an exterior surface, the interior surface being formed by the exterior surface of a capacitor bushing fixed by a disc to the tank of the transformer and the exterior surface, constituted mainly by a frustoconical insulating wall which shields the capacitor bushing, is inserted in the metallic casing of the device and can be fixed by its base to that casing.
In the examples of connections described in French Pat. No. 2,223,801 the frustoconical insulating wall is fixed by its base to an intermediate plate integral with the metallic casing of the device. A metallic bellows completes the exterior surface delimiting the volume of the jacket. It is disposed round the capacitor bushing and fixed by one end to the disc of that capacitor bushing which is integral with the tank of the transformer and by the other end to the intermediate plate. Surfaces of the base of the frustoconical insulating wall and of the intermediate plate in contact with each other make the interior volume of the jacket communicate with the interior volume of the device in a metallic sheath. A large-diameter annular seal is placed between these surfaces to provide sealing and to avoid gas leakages from the device towards the interior volume of the jacket.
Preferred embodiments of the present invention prevent leakage of the insulating gas into the interior volume of the jacket by means of a modification to the shape of the insulating wall's base in the above-mentioned seal.